Method of coating paper or other sheet material with surface layers of different coating compositions

ABSTRACT

A method of coating paper or other sheet material with surface layers by applying different coating compositions to each side of a travelling sheet by feeding the sheet between two opposed members defining a press nip formed of a resilient thin blade having a sharp edge engaging the sheet as one member of the press nip, and a rotatable roller supporting the sheet on one side as the other member of the press nip. A first coating composition is applied to one side of the sheet from a dam defined on one side by the sheet and on the other side by the blade, whereas the second coating composition is applied to the opposed side of the sheet by means of contact transfer of said second coating composition, which has been previously applied to the surface of the roller.

United States Patent [191 Wallstn [451 Aug. 12, 1975 METHOD OF COATINGPAPER OR OTHER SHEET MATERIAL WITH SURFACE LAYERS OF DIFFERENT COATINGCOMPOSITIONS [75] Inventor: I-Ians Ivar Wallstn, Saffle, Sweden [73]Assignee: AB Inventing, Saffle, Sweden [22] Filed: Feb. 28, 1973 [21]Appl. No.: 336,777

[30] Foreign Application Priority Data Mar. 13, 1972 Sweden 3150/72 [52]US. Cl. 427/211; 427/356; 427/361 [51] Int. Cl. BOSC 9/04 [58] Field ofSearch 117/68, 111 F, 111 R; 1 18/204 [56] References Cited UNITEDSTATES PATENTS 2,946,307 7/1960 Warner 117/68 3,104,182 9/1963 Schneideret a1. 118/204 3,282,726 11/1966 Seligsberger 117/68 3,483,017 12/1969Korpman 117/68 1/1970 Wallsten 117/68 7/1972 Spearin et a1 117/68 [5 7ABSTRACT A method of coating paper or other sheet material with surfacelayers by applying different coating compositions to each side of atravelling sheet by feeding the sheet between two opposed membersdefining a press nip formed of a resilient thin blade having a sharpedge engaging the sheet as one member of the press nip, and a rotatableroller supporting the sheet on one side as the other member of the pressnip. A first coating composition is applied to one side of the sheetfrom a dam defined on one side by the sheet and on the other side by theblade, whereas the second coating composition is applied to the opposedside of the sheet by means of contact transfer of said second coatingcomposition, which has been previously applied to the surface of theroller.

2 Claims, 3 Drawing Figures PATENTEU AUG 1 2 ms SHEEF METHOD OF COATINGPAPER OR OTHER SHEET MATERIAL WITH SURFACE LAYERS OF DIFFERENT COATINGCOMPOSITIONS According to a known method, described in US. Pat. No.3,489,592, a satisfactory coating result canbe obtained by guiding a webof material, for example paper, in a substantially vertical directiondownwardly through a press nip which is formed between a thin, flexibleblade in the form of, for example, a steel blade with a sharp edge and arotating roller, the spaceybetween the blade and the roller forming adam filled with the coating composition. Immediately after passingthrough said nip the paper web is deflected toward the side at which theblade is located, so that an angle is formed between the tangent of theroller and the downward passing portion of the web thereby avoiding afilm splitting. This known method however only permits the use of thesame coating compositions on both sides of the paper web. The reason forthis is obvious and is due to the fact that the same dam surrounds thepaper web and that it has been found extremely difficult to arrange asuitable device to separate the dam, for example into two dams, one foreach side of the web, so as to permit a coating with different coatingcompositions on each side of the paper web.

The present invention intends to exploit the favourable effects of thisknown blade coating method, while avoiding the disadvantages in thatthis'known method does not permit coating with different coatingcompositions on opposite sides of the paper web.

According to the present invention a first coating composition isapplied to the side of the sheet facing the blade from a dam defined onone side by the sheet and on the other side by the blade and a secondcoating composition is applied to the opposite side of the sheetabutting the roller by means of contact transfer of said second coatingcomposition, which has been previously applied to the surface of theroller.

Further features and advantages of the invention will be apparent fromthe following description of embodiments thereof given by way of examplewith the accompanying drawings, in which:

FIG. 1 shows a prior art device according to US. Pat. No. 3,489,592

FIG. 2 shows an apparatus for performing the present invention and FIG.3 shows a further apparatus suitable for performing the presentinvention.

In FIG. I the reference numeral 4a indicates the path of a paper webbefore the nip between a blade 3 which is attached in a blade holder 2and a rotating roller 1. The path of the paper web after passing the niphas been indicated by reference numeral 4, and 5 indicates a guideroller. According to this prior method particularly good results havebeen obtained when blades in the form of steel blades with a sharp edgeand a thickness of between 0.2O.7 mm are used.

It should be clear from FIG. 1 that this prior art device only permitsthe use of the same coating compositions on both sides of the paper web.The reason for this is obvious and is due to the fact that in thisdevice the same dam 11 surrounds the paper web. In practice it has beenfound extremely difficult to arrange a means to separate the dam I], forexample into two separate dams, one for each side of the web, so as topermit coating with different coating compositions.

, The presentinvention relates to a method of enabling simultaneouscoating of both sides of the paper with two different compositionswithout the compositions being mixed. FIG. 2 shows a paper guide roller10, over which the paper web 4b is led generally downwardly towards thecoating means. The paper web meets the roller 1 at a point 9, this pointlying above the horizontal surface of the coating composition in the daml 1 which is formed between the blade 3 in the holder 2 and therollersurface l.

The paper web is drawn over the blade edge 3 at an obtuse angle withrespect to the roller radius at the point of contact of the blade withthe roller. A second rotating roller 6 is pressed with a suitablepressure against the roller 1. A device 7 sprays the desired secondcoating composition onto the roller 6 which distributes and transfers acertain amount of the composition onto the roller surface 1.

At the contact point 9 the transfer of the second coating compositionfrom the roller surface 1 to the side of the paper facing the rollersurface is initiated, partially in the form of absorption. By suitablechoice of base paper, speed, coating composition and the quantity ofthis coating composition supplied, the desired quantity of coatingcomposition can be transferred to the surface of the paper web withoutany excess being pressed out, for example laterally, before the nip inthe dam, thus causing the compositions to mix. In order to prevent amixing of the different coating compositions, it is also advisable toensure that the second coating composition applied on the roller 1 islimited laterally so that it has the same width as the paper web 4b oris narrower. This can be achieved, for example, by making the roller 6narrower than the paper web 4b or by providing the roller with suitablescraping means to remove the coating composition along each edge of theroller 1 or 6.

The side of the paper facing away from the roller 1 is coated with afirst coating composition in the dam 1 l in conventional manner, i.e.the blade 3 doses and smoothes out the coating composition on this sideof the paper.

It is easily understood that the arrangement described permits differentcoating compositions to be coated on each side of the web without riskof the compositions becoming mixed.

Various arrangements are feasible within the scope of the invention forapplying the coating compositions on the roller side and FIG. 3 shows adifferent embodiment where reference numerals 6 and 8 indicate twodistributing rollers which can preferably be adjusted in relation toeach other and the roller 1 and which can preferably be run at differentspeeds. The second coating composition is supplied through the pipe 7and the arrangement shown permits careful control of the layer of thesecond coating composition applied on the roller surface 1.

What I claim is:

l. A method of coating paper or other sheet material with surface layersby applying different coating compositions to both sides of a movingsheet by feeding the sheet between two opposed members defining a pressnip formed of a resilient thin blade having a sharp edge comprising onemember of the press nip and a rotatable roller supporting the sheet onone side comprising the other member of the press nip, said stepscomprising:

applying a first coating composition to one side of the sheet by meansof contact transfer of said first coating composition, which is appliedto the surface of said roller; said first coating applied to said rollerbeing limited laterally so that the width of the applied layer isnarrower than the width of the sheet; applying a second coatingcomposition to the other side of the sheet from a dam arranged above thepress nip and defined on one side by the sheet and on the other side bythe blade; said sheet being brought into engagement with the surface ofsaid roller before entering said nip to prevent the first coatingcomposition from entering the dam and thus being mixed with the secondcoating composition in said dam.

2. The method of claim 1 further comprising the step of deflecting thesheet at an angle to its direction of travel over the sharp edge of saidthin blade to prevent the coating formed by the first coatingcomposition from peeling.

1. A METHOD OF COATING PAPER OR OTHER SHEET MATERIAL WITH SURFACE LAYERSBY APPLYING DIFFERENT COATING COMPOSITIONS TO BOTH SIDES OF A MOVINGSHEET BY FEEDING THE SHEET ETWEEN TWO OPPOSED MEMBERS DEFINING A PRESSNIP FORMED OF A RESILIENT THIN BLADE HAVING A SHARP EDGE COMPRISING ONEMEMBER OF THE PRESS NIP AND A ROTATABLE ROLLER SUPPORTING THE SHEET ONONE SIDE COMPRISING THE OTHER MEMBER OF THE PESS NIP, SAID STRIPSCOMPRISING: APPLYING A FIRST COATING COMPOSITION TO ONE SIDE OF THESHEET BY MEANS OF CONTACT TRANSFER OF SAID FIRST COATING COMPOSITION,WHICH IS APPLIED TO THE SURFACE OF SAID ROLLER, SAID FIRST COATINGAPPLIED TO SAID ROLLR BEING LIMITED LATERALLY SO THAT THE WIDTH OF THEAPPLIED LAYER IS NARROWER THAN THE WIDTH OF THE SHEET, APPLYING A SECONDCOATING COMPOSITION TO THE OTHER SIDE OF THE SHEET FROM A DAM ANANGEDABOVE THE PRESS NIP AND DEFINED ON ONE SIDE BY THE SHEET AND ON THEOTHER SIDE BY THE BLADE, SAID SHEET BEING BROUGHT INTO ENGAGEMENT WITHTHE SURFACE OF SAID ROLLER BEFORE ENTERING SAID NIP TO PREVENT THE FIRSTCOATING COMPOSITION FROM ENTERING THE DAM AND THUS BEING MIXED WITH THESECOND COATING COMPOSITION IN SAID DAM.
 2. The method of claim 1 furthercomprising the step of deflecting the sheet at an angle to its directionof travel over the sharp edge of said thin blade to prevent the coatingformed by the first coating composition from peeling.